A solar cell is a device which converts electromagnetic radiation (in general sunlight) into electric energy. The energy conversion is based on the absorption of radiation in the solar cell, thereby generating positive and negative charge carriers (electron-hole pairs). The generated charge carriers are furthermore separated from each other, and are transferred to different contacts.
Common solar cells are made of the semiconductor material silicon, and comprise a p-n junction which is arranged between a so-called “emitter” and a so-called “basis”. By means of the p-n junction, an inner electric field is provided which serves for the above mentioned charge carrier separation. Such a photovoltaic structure may e.g. include a thin n-conductive layer (n-type emitter) and an adjacent p-conductive region (p-type basis). The different electric properties of emitter and basis may be defined by respective doping.
One main demand of solar cells is to provide a high efficiency and a high energy conversion factor. The development of solar cells therefore tends to minimize potential losses such as optical losses (due to e.g. reflection, shadowing effects, etc.) and recombination losses (recombination of the produced charge carriers).
Concerning reflection losses, it is e.g. known to provide an antireflection layer for the solar cells which is also referred to as ARC-layer (antireflective coating). For this purpose, a reflection minimizing silicon nitride layer (SiN) is typically deposited on silicon solar cells after producing the emitter, e.g. by depositing a hydrogen-rich silicon nitride layer (SiNx:H). By performing a temperature step (which is performed in the course of making contacts and which is also referred to as “firing”), hydrogen of the silicon nitride layer may be introduced into the solar cells, thereby performing a passivation of defects and making a reduction of recombination losses possible. However, the deposition of silicon nitride which is conventionally carried out by means of a PECVD-process (plasma enhanced chemical vapor deposition) is associated with high effort and high costs.
U.S. Pat. No. 4,592,925 discloses a solar cell having a protective coating consisting of polyimide. Apart from the protective coating, the solar cell comprises an inorganic antireflection layer which is arranged on a substrate of the solar cell. A combination of metal oxides and a combination of a metal oxide and silicon oxide are disclosed as materials for the antireflection layer.
U.S. Pat. No. 4,361,598 describes a method of producing an inorganic antireflection layer for a solar cell. In the method, a solution comprising different components is applied to the solar cell, and a heating step is carried out in order to remove solvents and organic components. Furthermore, it is described to leave a rest of organic components in the inorganic antireflection layer if necessary.